The goal of this research is to understand the mechanisms which the auditory system uses to determine the vertical direction of a sound source. These mechanisms are known in a general way to include an acoustic stage associated with the external ear as a receiving antenna for sound, auditory stages associated with the neural encoding of the waveform of sound and isolation of the specific acoustic dimensions carrying information about vertical direction, and a spatial perceptual stage associated with the transformation of neurally-encoded acoustic information into a specific neural representation of vertical direction itself. We presently lack an understanding of important aspects of each stage as well as how these stages are articulated together to form a working unit serving spatial auditory perception in mammals, including humans. This research is intended to develop a full description of the process of vertical localization in a mammal, taking advantage of the relative exaggeration of vertical- localizing capabilities in echolocating bats, which makes them ideal biological models for such experiments. Spatial perception may be mediated by neural mechanisms that undergo continuous recalibration through a kind of neural plasticity. Such a mechanisms associated with sound localization in a mammal may have clinical significance as an instance of plasticity in an adult, with implications for recovery of brain function after injury. The experiments will measure the directional information encoded by the external ear in sounds reaching the ear-drum, will determine the effects of manipulation of the external ear on the direction and accuracy of vertical localization, and will explore how vertical position is represented in the auditory nervous system.